1. Field of the Invention
The present invention relates to a fundus imaging apparatus and, more particularly, to a fundus imaging apparatus which uses infrared light as an observation light source and white light as an imaging light source.
2. Description of the Related Art
A fundus imaging apparatus, in particular a non-mydriatic fundus camera, generally uses infrared light as an observation light source to prevent the constriction of the pupils for an object being examined, and visible light as an imaging light source to obtain a color image.
As an infrared light source, an infrared light component extracted from light from a white halogen lamp through an optical filter has been used. Advances in LED technology, however, have recently begun to allow the single use of an infrared LED. As a visible light source, an Xe tube is still used to instantaneously obtain a sufficient amount of light.
Recently, even a white LED which emits a sufficient amount of light has been developed. This has increased the possibility of implementing a visible light source using a white LED.
Japanese Patent Laid-Open No. 07-008459 discloses a technique for mechanically switching between infrared light and visible light by switching an optical filter to be placed in front of a light source for emitting light with a broad wavelength between an infrared transmission filter and a visible light transmission filter.
Japanese Patent Laid-Open No. 2008-212327 discloses a technique for obtaining an annular surface light source by alternately arranging infrared LEDs and white LEDs in an annular form. Infrared light and visible light are electrically switched.
Japanese Patent Laid-Open No. 2008-212375 discloses a technique for eliminating light source irregularity by rotating LED light sources discontinuously arranged in an annular form at the time of imaging.
In general, an observation light source and an imaging light source are selectively used by electrical switching, with an optical path being divided by a dichroic mirror. However, the intervention of the dichroic mirror causes a light amount loss. In addition, dividing the optical path requires to prepare optical paths at two portions, resulting in an increase in space for the optical paths. This leads to increases in apparatus size and the complexity of the structure and components.
According to Japanese Patent Laid-Open No. 07-008459, a compact light source called an LED light source does not exhibit a broadband characteristic as a light emission characteristic, and hence cannot be a light source which covers light ranging from infrared light to visible light. In addition, this device needs to prepare two optical filters in addition to a light source. That is, the device includes many constituent elements and has a complicated arrangement.
According to Japanese Patent Laid-Open No. 2008-212327, since infrared LEDs and white LEDs are alternately arranged on one circumference, the pitches between the infrared LEDs and between the white LEDs are large. For this reason, this light source cannot be a satisfactory light source as an observation/imaging light source required to provide uniform illumination in an annular form.
The light source disclosed in Japanese Patent Laid-Open No. 2008-212375 may possibly be put to practical use as an observation light source owing to an afterimage phenomenon. When, however, using this light source as an imaging light source, it is necessary to prolong the exposure time. This leads to image blur due to fixation disparity. It is therefore impossible to obtain a captured image with sufficient quality.
In consideration of the above problem, the present invention provides a technique of switching a plurality of light sources with a compact, simple arrangement while reducing a light amount loss.